Multi-million gallon storage tanks are commonly built with vertical walls of poured concrete. These walls are often stressed with wires, cables or bars. The wires, cables or bars are placed over a layer of shotcrete or gunnite. To ensure the shotcrete or gunnite adheres to the vertical tank walls, the walls are roughened or texturized by removing the top layer of material from the concrete surface. This is currently done by using sand blasting, bead blasting, or manual spraying with high pressure water.
The blasting methods leave a large amount of residue and can create clouds of dust, both of which are undesirable. Further, construction schedules do not allow much time to texturize the tank surface, and these tanks are very large: hundreds of feet in diameter and tens of feet high. To cover an adequate surface area in the time required, the blasting equipment is large, bulky, heavy and very noisyxe2x80x94all of which are undesirable. Efforts to reduce environmentally objectionable aspects such as dust clouds have resulted in large and heavy blasting recovery systems being used. But these systems are noisy, and leave blasting beads or sand distributed around the tank.
The manual water spraying is slow and produces inconsistent results because it is manually operated. The force from the manually operated sprayers is very large and can cause a sore shoulder if the spray guns are used for any length of time. Further, it requires positioning an operator around the tank wall and that poses some risk that the operator can fall off the support. Additionally, the operator must wear sound deadening headgear because of the noise, and that presents safety hazards.
There is thus a need for an improved way to quickly and safely texturize the vertical surfaces of these large storage tanks. There is a further need to texturize these tank walls while leaving no, or minimal residue. Moreover, there is a need to uniformly texturize the walls in order to avoid localized unbonded areas of shotcrete or gunnite.
It is therefore an object of this invention to provide a uniformly texturized surface on the vertical tank wall, with minimal environmental impact and where possible taking advantage of existing tank construction equipment. These and other objects of the invention are achieved by the following invention.
A method for texturizing an exterior surface of a cylindrical concrete storage tank is provided by placing a rotating spray nozzle assembly having a plurality of nozzles so the nozzles maintain a predetermined distance from the tank surface during operation of the nozzles. The nozzle assembly is moved over the cylindrical surface while maintaining the predetermined distance and while forcing a jet of water through the nozzles with sufficient velocity and flow to remove an exterior layer of concrete from the surface along a strip having a width and a length, in order to provide a predetermined roughness to the surface. Preferably, but optionally, the method preferably fastens the nozzle assembly to a structure that is constrained to move around a circumference of the tank, and further fastens the nozzle assembly to a moveable platform on the structure which platform can move along a vertical axis. Preferably the method moves the structure and nozzle assembly around the circumference of the tank as moves the platform and nozzle assembly along the vertical axis. Preferably, the nozzle assembly moves in a spiral pattern around the tank so that strips of removed material slightly overlap for substantial portions of the length of the strips. Ideally, the nozzle assembly moves in a spiral pattern around the tank so that the strips of removed material do not overlap for substantial portions of the length.
The method can further comprise viewing the strip through a camera to obtain information for use in obtaining the predetermined roughness of the surface. Further, the water flows through the nozzles at a pressure, and the pressure is varied to compensate for wear of the nozzles and maintain the predetermined roughness of the surface. Advantageously over 90% of the surface of the storage tank is roughened by this method, and preferably over 95% is textured.
There is thus advantageously provided an improved method of making a concrete storage tank. The method includes forming a cylindrical tank having a vertical wall made of concrete, the tank having a footing extending radially outward from the walls. A gantry is tethered from a center pin extending from the roof. The gantry is configured to move around a circumference of the tank on the base. The gantry has a platform that can be moved upwards and downwards relative to the gantry and also has a spray nozzle assembly mounted to the platform so the nozzle assembly can move around the tank with the gantry, and up and down an exterior surface of the tank relative to the gantry. The nozzle assembly is moved over the exterior surface of the tank at a predetermined distance from the surface while spraying high pressure water through the nozzle assembly to provide a predetermined roughness to the exterior surface of the concrete over at least 90% of the surface. A coating material is then sprayed on the roughened surface. Cables, bars or wires may then be placed over the roughened surface covered by the coating material.
The above method also preferably places the spray nozzle assembly in fluid communication with a source of water through an opening in the top of the tank, although other sources of the water can be used. In order to prevent unacceptable damage to the wall, the nozzle assembly advantageously moves at a speed which is monitored and wherein the water pressure to the nozzle assembly is maintained at a pressure selected to avoid unacceptable roughening of the concrete wall. This can be achieved by comparing a signal representative of a rate at which the gantry is moving with a signal representative of a predetermined rate of travel, and varying the pressure of the water to the nozzle assembly and/or the speed of the gantry in order to vary the roughness of the wall produced by the nozzle assembly.
These and other methods are preferably implemented using an apparatus having a gantry with a wheel in contact with at least one of a surface of the tank or base to position the gantry relative to the tank, and a motor in driving communication with the wheel to move the gantry around the tank. A platform is mounted on the gantry and configured to move relative to the gantry. A rotating spray nozzle is mounted on the platform a sufficiently close distance to the surface of the tank to abrade and remove the surface when high pressure water is sprayed through the nozzle. Preferably, at least one spacing wheel is provided in a fixed position relative to the nozzle and in contact with the wall of the tank to control the distance between the nozzle and wall. A pump is mounted on the gantry and in fluid communication with the nozzle. The pump is sized to provide water to the nozzle at a flow rate and pressure sufficient to remove at least the top layer of concrete on the tank wall opposite the nozzle.
The apparatus preferably, but optionally may have a controller having a first input representative of a speed at which the nozzle moves relative to the tank and having a second input representative of the water pressure at the nozzle, and has an output signal representative of a desired engine speed to achieve a pressure at the nozzle that is not sufficient to remove concrete from the tank wall opposite the nozzle. Preferably, the pump is sized to provide at least two gallons per minute of water at over 20,000 pounds per square inch to the nozzle, with the preferred pressure being about 36,000 to 40,000 psi. Advantageously as the nozzle removes a strip of material from the wall, a camera is supported by the gantry and located and orientated to provide an image of the strip of material shortly after the strip is formed by the nozzle. An operator can adjust the water pressure, or the speed between the nozzle and wall, or the distance between the nozzle and the wall, in order to vary the amount of texturing. Additionally, a shield is preferably located intermediate the nozzle and the platform, with the shield being configured to block a majority of the debris ejected from the walls from hitting the platform during use of the apparatus.
Preferably the spacing between the nozzle and the wall being textured is maintained using a roller connected to a frame to which the nozzle is connected, the roller being located so it can be placed in contact with the wall adjacent the nozzle to maintain a predetermined distance between the nozzle and the wall. The nozzle is slidably mounted to allow movement relative to the platform along an axis generally perpendicular to the wall, and preferably that movement can be controlled by an operator to allow remote adjustment in order to vary the texturizing of the wall.